The invention relates to a method of evaluating the effluent of a hydrocarbon well by means of a multiphase flowmeter. The invention also relates to an installation implementing such method.
When operating an oil well, it is necessary to monitor a large number of parameters concerning the multiphase fluid that flows out from the well. Such parameters vary over time, and the operating conditions must be adapted to take into account such variation.
The flow rates of the various phases contained in the fluid (e.g. a gas phase constituted by gaseous petroleum and two liquid phases constituted by water and liquid petroleum) are among the parameters to be monitored. Such monitoring may be performed either continuously, or periodically, e.g. every two or three months.
A first known technique for measuring the flow rates of the various phases of the fluid flowing out from an oil well consists in measuring the flow rates separately once the various phases of the fluid have been separated. In which case, the fluid passes successively through a plurality of separators in which gravity is used to separate the gas phase from the liquid phases, and then to separate the liquid phases from each other. The flow rates of each of the phases can thus be measured separately at the corresponding outlets of the separators.
In such existing flow-rate measurement installations, valves are placed downstream from the flowmeters provided to measure the separate flow rates of the various phases, in the outlet piping of the separators. Such valves serve to regulate the level of the interface between the phases to be separated inside the separator, and to regulate the pressure in the separator to a reference value.
That type of installation suffers from the drawback of taking up a particularly large amount of space because of the large dimensions of the separators.
For that reason, research and experimentation is being done with a view to measuring the flow-rates of the various phases of the oil well effluent by means of a multiphase flowmeter placed directly in the piping via which the fluid flows out from the well. Such flowmeters take up significantly less space, thereby enabling them, in particular, to be moved from one well to another to perform periodic measurements on each of them.
There are numerous types of multiphase flowmeters. By way of example, mention may be made of the flowmeters described in French patent applications No 2 764 065 and 2 767 919.
When such a multiphase flowmeter is used, the pressure in the flowmeter is controlled entirely by the conditions at the wellhead, i.e. immediately at the outlet of the oil well, and by the conditions much further downstream in the production line, at the place where the various phases of the fluid are finally separated.